Face Detection: How does it work?

The latest and greatest feature that all camera manufacturers are up selling is the "Face Detection" technology. It's available in most of the new compacts and must say - it is impressive.

One of my friends recently bought "Canon 950 IXUS" which comes with the "Face Detection" technology. We tested it and it works very well. We were pretty amazed and being IT people, started asking ourselves - "how the hell it knows how many faces are in the frame"

After googling around for some time, I got some answers to this mind blowing technology.

How does FD work?

All digital cameras have computers built into them - we like to call them "Processors" and "Sensors". Auto Focus (AF) and Auto Exposure (AE) features are based on this computer and it's thinking power.

When we "half-press" the shutter button, a beem of light is sent from the camera to the subject to determine the focus range, exposure and ISO settings. Once the computer stores all the details, a "beep" sound comes which tells you that it is ready for the shot.

Face Detection (FD) also takes help of this same computer. Manufactures have prepared a database of millions of facial structures and it's relative positioning in the face. Some things that go into this database is:

- Structure of eyes
- Structure of nose
- Distance of eyes to nose
- Face size
- Color temprature of skin tones (Yes - we all have color temprature measured in "Kelvin", do a google on it as I cannot explain it here)

As soon as you "half-press" the shutter, the FD algorithm in computer takes image in the frame as input and compares with the facial structure database and color temprature of skin. If a match is found, then that object is focused.

FD can identify more than one face in frame - so if 5 of you are posing in as a group, FD will "main" focus the center subject and then "additional" focus on the subjects to either side of main subject.

So no more "out of focus" subjects and no more loosing opportunities due to lack of focus.

Does FD fail?

Yes, it is a very new technology and it does fail in certain situations.

- Low light situations
- Subjects not facing the camera
- Distance between two subjects very high

These are all very minor issues where FD fails. Manufactures are working towards the next generation FD technology that will solve most of these issues. Until then, switch off the FD in such situations and depend on the traditional "Focus-Recompose-Shoot" technique :-)

AIRC has a very nice article on this subject with pictures that will give a good understanding of how different brand of cameras implement FD.
http://www.adorama.com/catalog.tpl?article=052107&op=academy_new

Happy Face Detecting !!